I am relying on the fact that Bar Sport allows for 'all sorts of unrelated topics' in order to post it here. Not Arduino related, unless you are doing an Arduino sounding balloon. Here is my question:

Why is helium used over hydrogen for large lighter-than-air balloons? Yeah, I know it was a real, real bad idea for the Hindenburg, but that was an all-weather passenger aircraft with lots of people in suits and no parachutes. Helium is really, really expensive and the world loses whatever it uses. It's bad to waste helium. From a recent article:

http://www.dailymail.co.uk/sciencetech/article-2217412

Quote

But Thompson said on Wednesday the balloons cost several hundred thousand dollars each, and he estimated the team lost $60,000 to $70,000 in helium with the aborted jump.

That's a lot of money. If you are flying on a perfect day, and Felix certainly was, why not use hydrogen? Inflate the balloon remotely. After it is inflated, there really should be no danger that cannot be mitigated. And the dude does have a solid capsule and a parachute if he needs to bail. Maybe I am an idiot, but I would fly this on hydrogen, if the permeation of hydrogen through the balloon membrane isn't so much greater than helium that this is a technical obstacle.

If the ballon ruptures during inflation, what would be the correct course of action to ensure no one was engulfed in flames?

Compressed hydrogen gas violently escaping from its container produces enough energy to ignite the hydrogen. In other words, if you drop a wrench and it cracks a pipe or fitting you will be very lucky if your destination is the hospital.

If the ballon ruptures during inflation, what would be the correct course of action to ensure no one was engulfed in flames?

Compressed hydrogen gas violently escaping from its container produces enough energy to ignite the hydrogen. In other words, if you drop a wrench and it cracks a pipe or fitting you will be very lucky if your destination is the hospital.

If the balloon ruptures, I think mitigation would be to wait a few seconds, the hydrogen will be 50' off the ground by then and very soon afterwards at the top of the atmosphere.

But I had no idea about your last point, that does sounds dangerous and hard to mitigate.

Think about it, why does no one do it any more? Hydrogen is used to fule rockets, it combusts much easer than you think.From a ruptured ballon it would not dissipate in seconds, that's the physics of the situation.

Pure hydrogen does not burn let alone explode and released hydrogen or hydrogen mixed with air does need a spark to set it off.

The Hindenburg made quite a few trips before a design flaw caught up with it. Santos-Dumont was making frequent hydrogen blimp flights around 1900, he seemed to have a handle on how-to. It even became a big sport up to 1910 or so with fly-ins in Europe and the US that I know of. During WWI they used hydrogen for observation balloons and Zeppelins where going down in flames was due to enemy fire.

You can get sparks from static but hey they send instrumented balloons up on hydrogen all the time... I wonder how many of those burn up? It takes oxygen (or other oxidizer) mixed with hydrogen to have a problem, you could flush the bag out with dry nitrogen before putting the hydrogen in.

Where to get hydrogen? From a gas supply company. Liquid hydrogen in large quantities used to be about cheap as beer per volume. ;^) It should always be far cheaper than helium.

Most likely leakage. The Helium Molecule is larger than the Hydrogen molecule so it leaks less. Pump any other gas into a container and it stays there. Pump hydrogen in and if there is ANY thought of a crack it will all leak out.

Another possibility is the amount of expansion of hydrogen over helium.

And for the volumn it might just be too dangerous...

Hyrogen will burn in almost any mixture with oxygen. Some gases can actually self smother because they need a critical mixture to burn.

Most likely leakage. The Helium Molecule is larger than the Hydrogen molecule so it leaks less. Pump any other gas into a container and it stays there. Pump hydrogen in and if there is ANY thought of a crack it will all leak out.

Another possibility is the amount of expansion of hydrogen over helium.

And for the volumn it might just be too dangerous...

Hyrogen will burn in almost any mixture with oxygen. Some gases can actually self smother because they need a critical mixture to burn.

I mentioned the permeation of hydrogen in my original post. I know that is a problem with hydrogen gas. It's also a problem with helium. I wonder which is worse. Hydrogen gas is diatomic. Helium is monoatomic. The ratio of molecular weights is slightly less than 1:2 not 1:4. I wonder what the molecular sizes are.

For a "near space" project hydrogen is fine.Here in Australia the Bureau of Meteorology release 2 weather balloons a day.They fill them with hydrogen, because it's cheaper.When you fill your balloon you need to do it fairly slowly, static is a BAD thing.

The Hindenburg gave hydrogen a bad rep!

I've filled quite a few balloons with hydrogen, all the times I've set myself on fire it was doing way dumber stuff.

You can make hydrogen from electrolysis or chemical reactions, like zinc in hydrochloric acid.Most folks don't realise all the helium we have is all the helium we have!It's why the USA could only fill the Los Agngeles OR the Akron, but never both!There is quite a bit of controversy about the use of helium right now.The USA has a stockpile, some scientists are cautioning that we are running out.

For MIG welding ARGSHIELD is way cheaper than helium, it's not as good, but you really only need helium if you are MIG welding aluminium.

Right now I'm going through all the rigmarole of getting CASA approval for a near space balloon.The pricks are making me jump through more hoops than a dog and pony show!

When/if I finally get approval my balloon is going to be filled with hydrogen.BOC gasses will sell you a cylinder full, it's no big deal.

Joule-Thomson appear to disagree with you...http://en.wikipedia.org/wiki/Joule%E2%80%93Thomson_effect

I have first-hand knowledge that escaping hydrogen can ignite in the way I've described.

huh.

Quote

Helium and hydrogen are two gases whose Joule-Thomson inversion temperatures at a pressure of one atmosphere are very low (e.g., about 51 K (?222 °C) for helium). Thus, helium and hydrogen warm up when expanded at constant enthalpy at typical room temperatures.

OK, so there are some special cases.

I do know that the plumbing for a balloon fill connection gets cold. We dump pretty much a whole tank of He into a balloon, going from 2200PSI to 1ATM in the process.